Algicide
Offers New Way to Fight Off-Flavor in Catfish

Catfish farmers made sad and blue by
blue-green algae that cause off-flavors in their fish may soon get some relief.
Agricultural Research Service scientists
have discovered a natural-based algicide that not only kills the algae in fish
ponds, but is notably safer for other pond life when compared to current
treatments.

The research targets a species of blue-green algae prevalent in Mississippi,
home to half of the nation's catfish farms. This algal species produces a musty
compound that can be absorbed by the catfish, giving them a "muddy"
type of off-flavor.

Currently, catfish farmers choose between two chemical treatments for the
$50-million-per-year problem: copper sulfate, the only
U.S. Environmental Protection Agency-approved
algicide for such use on a permanent basis; and diuron, a chlorine-based
herbicide that can be used only with government permission on an annual basis.
Both of these treatments can be toxic to most phytoplankton, including green
algae that do not cause off-flavor.

In laboratory tests, the algicide was 40 times less lethal to green algae
than diuron. It also rapidly dissipated from pond water within hours, whereas
diuron can be detected for weeks after application.

After showing great potential in the laboratory and in fiberglass enclosures
placed in ponds, the algicide will now be tested in catfish-filled ponds. If
approved as a biopesticide, the new algicide may be available in two to three
years. ARS is seeking a commercial partner to fully develop and commercialize
the algicide.

More information can be found in the
April 2003 issue of
Agricultural Research magazine.